Speedometer-magnet compensator



l 623 558 April 5 1927' F. G. scHwElsTH/u. l

SPEEDOIE'PE3R.k MAGNET COMPENSATOR original Filed Feb. 12. 19,25

Patented Apr. Y 5, 1927.

UNITEn staresrnnn GEORGE SGHWEISTHAL, onor-Ireneo, trainers, nssrenon rio lsrn,waar-wan- NER SIEEDVCMETER CORPORATION, F CHICAGO, ILLINGIS, A` CORPORATION OFr VIRGINIA.

Appieation i'led February 12, 1925, Serial No.` 8,669. Renewed December 12, 1925.

Y The purpose of this invention is to provrde an improved lcoi'npensatmg devlce for permanent magnets such as those employed in tachometersland speedometers, the compensator being particularly designed and shown for thermost'atie operation to make the propercorrection in the magnet throughout a range of temperature change. rlhe vinvention consists in certain featuresand l0 elements of construction in combination as lherein shown Vand described and as indicated by the Vclaims. Inthe drawings `Figure 1 is a top plan view of a tachom` eter magnet with its yassociated mount and thermostatic compensating device fitted with p the `improvement embodying this invention. .-Figure 2 is a diametral'section taken as indicated at line 2 2 on Figure 1.

Figure 3 is a section taken as indicated at line 3 3 onV Figure 1.

Figure 4 is a fragmental perspective view for indicating more clearly the relation of the. antifriction device to the associated parts. Y

In tachometers and speedometers employing permanent magnets of annular form it is standard practice to provide temperature compensation for such magnets by overlapping the gap of the magnet with a movable shunt plate which is rendered adjustable by thermostatic means for varying its overlap on the magnet polesfand thus varying the portion of the flux which is diverted through the shunt plate. This compensating device is so designed as to maintain the magnetic field outside the magnet at a substantially constant strength notwithstanding the change of permeability which occurs upon change of temperature. A device of this nature is shown in Letters Patent No.1,155,34c6, issued October 5, 1915.

When a compensating shunt plate of this character is mounted in actual contact with the face of the magnet it is found that there is some tendency for it-to stickV to the maglnet so as to. require considerable force to slideit over the magnet face for shifting its relation to the gap at the poles. This tends to prevent a. perfectly continuous compensation as the temperature varies, because it requires the thermostatic device to accu- Vmulate the necessary force through a change of several degrees of temperature before it can initiate movement Vof the shunt plate. The present invention therefore provides anti-friction means acting to hold the shunt plate out of contact with the face of` the magnet and thus permitting itto be lshifted much more readily.

In the drawings the` usual annular-form of magnet is shown at 1 with a radial rift or slot at 2 between its poles. The magnet s supported on a mount, 3, usually of die cast non-magnetic metal, filling the center of the annular magnet, 1, and itself secured to the drive shaft, 4. The shunt Vplate is shown at 5 partially overlapping the' gap, 2. Hthin a central space, 6, in the mount, 3, a. curved `bi-nietallic bar, 7,. serves as the thermostatic means for shifting the shunt plate, Said bar is anchored to the mount at one end bypa screw, 8, and at the other end is formed with a lug, 9, shown as passing through a fitted aperture in the plate, 5, and riveted over for permanent attachment thereto. i

In the portion of the mount, 3, which eX- tends between the central opening, 6, and the magnet, 1, a steel ball, 10, is poclreted in a trough or recess, 11, directly below the e Vof the magnet, 1. As the thermostatic bar, 7,

shifts the plate, 5, in circumferential direction the ball rolls slightly inthe recess, 11, but the range of movement is so limited that the ball is always retained under the plate, 5, for holding it out of Contact with the magnet face and preventing it from sticking to the magnet in opposition to the force of the thermostat, 7.

I claim:-

1. In a tachometer a permanent magnet and a non-magnetic mounting member by which the magnet is rotatively carried, a compensatingl shunt plate and means by which said shunt plate is carried by the mounting member for lapping themagnet adjacent its poles, automatic means to move said shunt plate relatively to said vmagnet poles, and means interposed between the mount and the shuntplate for spacing the Vshunt plate from the magnet pole, said means being adapted to move freely with with.

2. In a tachometer a split ring magnet, and a non-magnetic mount upon which it is carried, a compensating device, comprising a shunt plate, also carried by the mount and overlapping the gap between the magnet poles at one face of the latter; and means interposed between the mount and the free end ofthe compensating` member -for spacing the shunt plate from the magnet poles, said means being adapted to move freely with the shunt plate at the point of lodgement of the latter thereon.

3. In a tachometer a split ring magnet, a shaft for rotating it about its axis, a nonmagnetic mounting member secured to the shaft and centrally disposed in the magnet for carrying the latter. a Calibrating member secured to the mount at one end, and at the other end having a compensating shunt plate overlappingone face ot the magnet adjacent to its poles: means for moving the shunt plate with respect to the magnet poles, and a rolling member between the mounting member and the shunt plate, dimensioned for spacing the shunt plate from the magnet poles.

4. In a taehometer a split ring magnet, and a shaft rotating the magnet. a nonmagnetic mount secured to the shaft and centrally disposed in the magnet, a shunt plate lapping the magnet adjacent to its poles, a thermostatic device secured to the mount and to said shunt plate for moving the latter circumterentially with respect to the magnet to vary its overlap at the magnet poles, said shunt plate being extended from its connection to the thermostatic device across the non-magnetic mount for lapping the poles, and a rolling spacing member lodged in the mount under the shunt, dimensioned for spacing the shunt plate out otl Contact with the surface ot the magnet.

5. In a tachometer a permanent magnet, a mount b v which it is carried, a compensating shunt plate and thermostatic means by which the shunt plate is carried by the magnet mount tor movement of the shunt plate relative to the magnet poles, and antifriction means interposed between the magnet mount and the shunt for holding the shunt plate spaced away from the magnet poles.

6. In a tachometer, a permanent magnet. a non-magnetic mounting member by which the magnet is rotatively carried, a compensating shunt plate, thermostatie means by which said shunt plate is carried by the mounting member lapping the magnet adjacent its poles and for movement of said plate rotatively relative to said poles, and co-operating means between the mounting member and the shunt plate for holding the shunt plate spaced away from contact with the magnet.

FRED GEORGE SCHWEISTHAL. 

